Novel di- and tetra-substituted calix4arene derivatives bearing diacetylene moieties at the lower rim of macrocycle were synthesized
via
the Mitsunobu and Williamson reactions. The dealkylation of ...diacetylene moieties of calix4arene was for the first time discovered in the DMSO—hydrazine hydrate system. An important role in the dealkylation of diacetylene moieties is played by neighboring unsubstituted OH groups at the macrocycle. Blocking of OH groups with butyl substituents and elongation of the linker between the butadiynyl fragments and the macrocyclic platform significantly reduce the affinity of macrocycle to reductive cleavage. The unique reactivity of calix4arene in its reaction with hydrazine hydrate was demonstrated in comparison with a model conjugate of diacetylene with 4-
tert
-butylphenol. The reductive cleavage may proceed
via
the formation of pyrazole derivative of calix4arene. Pyrazole derivatives were the most reactive ones in the reaction with hydrazine hydrate among the studied isostructural calixarenes containing an active α-arylmethyleneoxy moiety. Results of performed quantum chemical calculations allowed us to propose a scheme for the reductive cleavage of oxymethylene derivatives of pyrazole with hydrazine hydrate.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In this work we report extensive DFT study of sydnone-alkyne cyclization which included investigation of the reaction mechanism, analysis of different factors affecting sydnone and alkyne reactivity ...as well as attempt to reproduce quantitatively experimental activation free energy. The calculations were performed for a set of 18 sydnone-alkyne reactions with a help of a semi-automatized workflow involving reagent preparation and generation of starting structures for a plausible transition state. Reconstructed reaction path supported two-step mechanism: cycloaddition followed by retro-Diels-Alder reaction. Since the latter had a tiny barrier, the cycloaddition step was predicted to be the rate-limiting. For the ensemble of reactions, calculations reproduce activation free energies extracted from experimental reaction rates (k) with the accuracy of 2 kcal/mol. Accounting for solvation effects didn't change the overall trend of activation free energies as a function of substituents. A series of statistical model linking logk and sydnones structure was built using Support Vector Regression and Multiple Linear Regression machine-learning methods coupled with different types of molecular descriptors; none of them demonstrated a good performance at cross-validation stage. Detailed analysis of different factors affecting reaction rate variation as a function of substituents revealed particular role of the charge on C3 atom in the sydnone moiety as well as of the size of the substituent at C3.
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•DFT study of sydnone-alkyne cyclization supports two-steps mechanism: cycloaddition followed by retro-Diels-Alder reaction.•A linear correlation between experimental and calculated activation free energies was observed.•Calculations reproduce experimental activation free energies with the accuracy 2 kcal/mol.•Charge on C3 atom in the sydnone moiety and size of the substituent at C3 significantly affect reaction rate.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this article, we consider cross-validation of the quantitative structure-property relationship models for reactions and show that the conventional k-fold cross-validation (CV) procedure gives an ...'optimistically' biased assessment of prediction performance. To address this issue, we suggest two strategies of model cross-validation, 'transformation-out' CV, and 'solvent-out' CV. Unlike the conventional k-fold cross-validation approach that does not consider the nature of objects, the proposed procedures provide an unbiased estimation of the predictive performance of the models for novel types of structural transformations in chemical reactions and reactions going under new conditions. Both the suggested strategies have been applied to predict the rate constants of bimolecular elimination and nucleophilic substitution reactions, and Diels-Alder cycloaddition. All suggested cross-validation methodologies and tutorial are implemented in the open-source software package CIMtools (
https://github.com/cimm-kzn/CIMtools
).
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
The search for neutrino events in correlation with gravitational wave (GW) events for three observing runs (O1, O2 and O3) from 09/2015 to 03/2020 has been performed using the Borexino data-set of ...the same period. We have searched for signals of neutrino-electron scattering and inverse beta-decay (IBD) within a time window of Formula omitted s centered at the detection moment of a particular GW event. The search was done with three visible energy thresholds of 0.25, 0.8 and 3.0 MeV. Two types of incoming neutrino spectra were considered: the mono-energetic line and the supernova-like spectrum. GW candidates originated by merging binaries of black holes (BHBH), neutron stars (NSNS) and neutron star and black hole (NSBH) were analyzed separately. Additionally, the subset of most intensive BHBH mergers at closer distances and with larger radiative mass than the rest was considered. In total, follow-ups of 74 out of 93 gravitational waves reported in the GWTC-3 catalog were analyzed and no statistically significant excess over the background was observed. As a result, the strongest upper limits on GW-associated neutrino and antineutrino fluences for all flavors ( Formula omitted) at the level Formula omitted have been obtained in the 0.5-5 MeV neutrino energy range.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We report the first direct QSPR modeling of equilibrium constants of tautomeric transformations (logK
T
) in different solvents and at different temperatures, which do not require intermediate ...assessment of acidity (basicity) constants for all tautomeric forms. The key step of the modeling consisted in the merging of two tautomers in one sole molecular graph (“condensed reaction graph”) which enables to compute molecular descriptors characterizing entire equilibrium. The support vector regression method was used to build the models. The training set consisted of 785 transformations belonging to 11 types of tautomeric reactions with equilibrium constants measured in different solvents and at different temperatures. The models obtained perform well both in cross-validation (Q
2
= 0.81 RMSE = 0.7 logK
T
units) and on two external test sets. Benchmarking studies demonstrate that our models outperform results obtained with DFT B3LYP/6-311 ++ G(d,p) and ChemAxon Tautomerizer applicable only in water at room temperature.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Industrial Detector of REactor Antineutrinos for Monitoring (iDREAM) is a 1 ton Gd-doped liquid scintillator detector mounted in the Kalinin nuclear power plant (Russia), 20 m from the 3 GW
VVER type ...commercial reactor. Antineutrinos are detected via inverse beta decay on protons. Beginning in 2021, the detector is collecting data both in reactor ON and OFF modes. The first iDREAM antineutrino results are presented, showing no doubt on the proper operation of the detector as a counting device.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Abstract
The paper is devoted to the description of the iDREAM
detector and its systems. iDREAM is a prototype detector designed to
demonstrate the feasibility of antineutrino detectors for remote
...reactor monitoring and safeguard purposes. Antineutrinos are
detected with a 1 ton liquid scintillator via inverse beta decay on
protons. In order to suppress cosmic muons, gamma and neutron
background, the detector is housed in a dedicated shielding. The
detector is installed at the Kalinin nuclear power plant (Russia),
20 m from the 3 GW
th
reactor core.
By the structural representation of a chemical reaction in the form of a condensed graph a model allowing the prediction of rate constants (log
k
) of Diels–Alder reactions performed in different ...solvents and at different temperatures is constructed for the first time. The model demonstrates good agreement between the predicted and experimental log
k
values: the mean squared error is less than 0.75 log units. Erroneous predictions correspond to reactions in which reagents contain rarely occurring structural fragments. The model is available for users at https://cimm.kpfu.ru/predictor/.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Optical metallography and electron microscopy have been used to analyze the structural changes in magnesium MA14 alloy subjected to processing that combines multistep isothermal forging and ...isothermal rolling. It has been found that forging of a bulk workpiece leads to the formation of a structure, 85–90% of which consists of recrystallized grains with an average size of less than 5 µm. Subsequent rolling results in a completely recrystallized structure with a grain size of 1–2 µm. It is shown that the resultant structural states are characterized by grain size nonuniformity inherited from the initial hot-pressed semi-finished product. The nature and features of crystallization processes that take place in the alloy during processing are discussed.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Semantic analysis of text collections was used to identify drugs with similar therapeutic activity. Natural language processing methods were applied to analyse > 2.5 mln texts from drug reviews (in ...English) found on patient forums and discussion boards. In order to obtain distributed word representations form the input data, a continuous bag-of-words type model was used. Such model is one of the word2vec models intended to analyse the natural language semantics. This allowed the assignment of a numeric vector to each drug name. A list of pairs of drugs with similar vectors was formed. An analysis of this list confirmed that similar word vectors correspond to either drugs with the same active compound or to drugs with close therapeutic effects that belong to the same therapeutic group. The chemical similarity in such drug pairs was found to be low. The suggested procedure was used to visualize the chemical drug space and in the search for compounds with potentially similar biological effects among drugs of different therapeutic groups.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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